Problem-based learning (PBL) is considered to improve students’ critical thinking (CT) skills. However, there are several obstacles to implementing this instructional model. PBL is highly time-consuming and creates a high cognitive load, so it is not suitable for all students, especially students with low prior knowledge. To investigate this problem, we conducted a quasi-experiment to study the difference in the improvement of CT skills between students who study using PBL and student who study using PBL with problem posing within-solution (PPWS). The sample of this research is 71 high school students in Mataram City. The result revealed that there was no difference in the enhancement of CT skill between students who learn using PBL and student who learn using PBL with PPWS. This means we can substitute PBL into PBL with PPWS to foster student CT skills.