Per IRS Instructions for Form 1120S, page 20:
Schedules K and K-1 (General Instructions)
Purpose of Schedules
The corporation is liable for taxes on lines 22a, 22b, and 22c, on page 1 of Form 1120S. Shareholders are liable for tax on their shares of the corporation’s income (reduced by any taxes paid by the corporation on income). Shareholders must include their share of the income on their tax return whether or not it is distributed to them. Unlike most partnership income, S corporation income is not self-employment income and is not subject to self-employment tax.