FORM 6-K

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Report of Foreign Issuer

Pursuant to Rule 13a-16 or 15d-16 Under

the Securities Exchange Act of 1934

For the month of

April, 2014

Commission File Number: 001-13240

Empresa Nacional de Electricidad S.A.

National Electricity Co. of Chile Inc.

(Translation of registrant’s name into English)

Santa Rosa 76,

Santiago, Chile

(562) 26309000

(Address of principal executive office)

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

Form 20-F   x             Form 40-F   ¨             

Indicate by check mark if the registrant is submitting the Form 6-Kin paper as permitted by Regulation S-T Rule 101(b)(1):

Yes   ¨             No    x             

Indicate by check mark if the registrant is submitting the Form 6-Kin paper as permitted by Regulation S-T Rule 101(b)(7):

Yes   ¨             No   x             

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

Yes   ¨             No   x             

If “Yes” is marked, indicate below the file number assigned to the registrant in connection with Rule 13g3-2(b): N/A

Empresa Nacional de Electricidad S.A. (the “Company”) is incorporating by reference the information and exhibit set forth in this Report on Form 6-K into the Company’s registration statement on Form F-3 (Registration No. 333-195009) filed on April 3, 2014.

Other Events

In connection with the Company’s offering of US$400,000,000 of its 4.250% Notes due 2024, the Company is filing the Underwriting Agreement dated April 10, 2014 by and between the Company and BBVA Securities Inc. and J.P. Morgan Securities LLC, as representatives of the several Underwriters named therein, as Exhibit 1.1 to this Report on Form 6-K.

2