Navigate to the Internal Revenue Service website, and enter "forms and publications" in the search box. Select the result titled "Forms and Publications."
Type "7004" into the search box. Select the result titled "Form 7004."
Fill out your name and contact information at the top of the form.
Type "25" in Part II, Section 1B, where it asks for the form code. This code indicates that you are asking for an extension to file your form 1120S. Do not check the boxes in Part II, Section 2 or 3.
Fill out the remaining tax information in Part III. As an S corp, your "tentative total tax" is likely "0." Note that you should not check the box in Part III, as your S corporation does not qualify under Regulations section 1.6081-5.
File Form 7004 by the regular due date of the tax return. The form can be filed electronically through the IRS e-file service or by sending the form to the appropriate Internal Revenue Service Center.