Heat oven to 350°F. Stir together flour, cocoa, baking soda and salt; set aside.
Beat butter and sugar in large bowl with mixer until fluffy. Add eggs and vanilla; beat well. Gradually add flour mixture, beating well. Stir in peanut butter chips. Drop by rounded teaspoons onto ungreased cookie sheet.
Bake 8 to 9 minutes. (Do not overbake; cookies will be soft. They will puff while baking and flatten while cooling.) Cool slightly; remove from cookie sheet to wire rack. Cool completely. About 4-1/2 dozen cookies.
Recipe by I'm At Home Baking! at http://imathomebaking.com/25-days-of-christmas-cookes-day-23-reeses-chewy-chocolate-cookies/