SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 6-K

Report of Foreign Private Issuer
Pursuant to Rule 13a-16 or 15d-16 of the
Securities Exchange Act of 1934

For the month of December 2014

Commission File Number 1-13758

PORTUGAL TELECOM, SGPS, S.A.

(Exact name of registrant as specified in its charter)

Av. Fontes Pereira de Melo, 40
1069 - 300 Lisboa, Portugal

(Address of principal executive office)

Indicate by check mark whether the registrant files or will file annual reports under cover Form 20-F or Form 40-F.

Form 20-F  x   Form 40-F  o

 Indicate by check mark whether the registrant by furnishing the information contained in this Form is also thereby furnishing the information to the Commission pursuant to Rule 12g3-2(b) under the Securities Exchange Act of 1934.

Yes  o   No  x

Announcement  |  Lisbon  |  15 December 2014

Clarification to the Market disclosed by Oi

Portugal Telecom, SGPS S.A. hereby informs on the clarification to the market disclosed by Oi, S.A., according to the company’s announcement attached hereto.

www.ptsgps.pt

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Oi S.A.

Corporate Taxpayers’ Registry (CNPJ/MF) No. 76.535.764/0001-43
Board of Trade (NIRE) No. 33.300.29520-8

Public-Held Company

MATERIAL FACT

Oi S.A. (the “Company” or “Oi”, Bovespa: OIBR3, OIBR4; NYSE: OIBR, OIBR.C), in accordance with article 157, paragraph 4 of Law No. 6,404/76 (the “Brazilian Corporation Law”) and the Brazilian Securities and Exchange Commission (Comissão de Valores Mobiliários — CVM) Instruction No. 358/02, informs its shareholders and the market in general that:

In line with the discussion on its conference call regarding its results for the third quarter of 2014, the Company remains focused on the operational turnaround process. Oi’s preliminary financial figures in the first two months of the fourth quarter of 2014 confirm the Company’s perception that the third quarter of 2014 would be the inflection point for the results of its business.

In this sense, the Company discloses the following indicators, in preliminary form and subject to audit, as follows:

The Company continues to execute its strategy of improving its balance sheet. The announcement of the execution of the share purchase agreement for the sale of PT Portugal SGPS S.A. (“PT Portugal”) — the effectiveness of which is conditioned on the pending approval of the shareholders of Portugal Telecom, SGPS, S.A. (“PT SGPS”) at a meeting scheduled for January 12, 2015 — together with the sale of another set of mobile towers concluded in December, will significantly reduce Oi’s net leverage, strengthening its financial flexibility.

The expected completion of sale of PT Portugal will allow Oi to participate in the industry consolidation process in Brazil, carefully assessing all the available alternatives in order to identify the most efficient structure in terms of value creation for its shareholders and for all of its stakeholders.

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Oi is one of the three integrated companies in Brazil and is very well positioned to face the industry challenges and to capture the market opportunities, leveraging its ability to provide convergent services by offering complete service packages to its customers. Oi’s extensive infrastructure, underpinned by a fiber network of over 300,000 km and with a high transmission capacity, is a unique strategic asset to support the growth of voice, video and data services, both fixed and mobile, in Brazil.

Finally, the Company reiterates its commitment to investors and the market to promote the migration of its shareholder base to BM&FBovespa’s Novo Mercado, through the merger of shares with Telemar Participações S.A., the evolution of its corporate governance and the diffusion of the Company’s shares, as already disclosed to the market through the Material Fact of September 8, 2014, as well as in the Notices to the Market of October 13 and 20, 2014 and November 10, 2014.

Rio de Janeiro, December 15, 2014.

Oi S.A.

Bayard De Paoli Gontijo

Chief Execute and Financial Officer and Investor Relations Officer

Special Note Regarding Forward-Looking Statements:

This communication may contain forward-looking statements. Statements that are not historical facts, including statements regarding the beliefs and expectations, business strategies, future synergies and cost savings, future costs and future liquidity, are forward-looking statements. The words “will,” “will be,” “should,” “could,” “may,” “should be,” “could be,” “may be,” “estimates,” “has as an objective,” “targets,” “target “goal,” “anticipates,” “believes,” “expects,” “forecasts,” “intends,” “plans,” “predicts,” “foretells,” “projects,” “points to” and similar expressions are intended to identify forward-looking statements and are subject to a number of risks and uncertainties. These statements reflect current expectations. In light of the many risks and uncertainties surrounding the offer, you should understand that we cannot assure you that the forward-looking statements contained in this communication will be realized. Undue reliance should not be placed on such statements.

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SIGNATURE

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

Date: December 15, 2014

FORWARD-LOOKING STATEMENTS

This document may contain forward-looking statements. These statements are statements that are not historical facts, and are based on management’s current view and estimates of future economic circumstances, industry conditions, company performance and financial results. The words “anticipates”, “believes”, “estimates”, “expects”, “plans” and similar expressions, as they relate to the company, are intended to identify forward-looking statements. Statements regarding the declaration or payment of dividends, the implementation of principal operating and financing strategies and capital expenditure plans, the direction of future operations and the factors or trends affecting financial condition, liquidity or results of operations are examples of forward-looking statements. Such statements reflect the current views of management and are subject to a number of risks and uncertainties. There is no guarantee that the expected events, trends or results will actually occur. The statements are based on many assumptions and factors, including general economic and market conditions, industry conditions, and operating factors. Any changes in such assumptions or factors could cause actual results to differ materially from current expectations.

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