This study investigates the integration of Generative AI (GenAI) into the Design Thinking (DT) process through a professional development workshop for K-12 educators. Using a pre-test and post-test design with 21 participants, the study examined changes in AI-related competencies, AI × DT application ability, and teaching practice. Paired-sample t-tests revealed significant im-provements across all dimensions, with the largest gain in AI × DT application, indicating en-hanced integration of AI into design processes. Item-level analysis showed significant improve-ments in empathy, testing, prompt engineering, and pedagogical confidence, while content gen-eration and future adoption intention showed no significant change, due to high baseline scores. These findings suggest that integrating GenAI into DT can shift educators from tool-level use to cognitively and pedagogically integrated applications, contributing a structured approach for AI-enhanced teacher training.