The present study introduced Ren'py software as a digital storytelling (DST) tool to explore the effective use of digital game design learning in promoting critical thinking among high school students. A sample of 46 high school students enrolled in "Thinking Utopia," an elective course in critical thinking for civics education, was put into groups of 3 to 4 for learning activities towards their collaborative designs of DST games. The course stretched across 9 weeks. Students' performance in critical thinking tests was also closely examined using paired-sample t-test analysis, which found no significant improvements; however, their interview responses were carefully studied using qualitative analysis and revealed that many of them agreed that the proposed collaborative activities for game script writing and for their collaborative designs of original hurdle questions have stimulated their critical thinking ability and contributed to the development of their other skills such as communication, problem-solving and media literacy.