Any apoptotic process in a keratinocyte. A keratinocyte is an epidermal cell which synthesizes keratin and undergoes a characteristic change as it moves upward from the basal layers of the epidermis to the cornified (horny) layer of the skin. [ GOC:mtg_apoptosis http://www.ncbi.nlm.nih.gov/pubmed/10201527 GOC:jc http://purl.obolibrary.org/obo/CL_0000312 ]