As stipulated in the "K to 12 Program" of the Department of Education, Philippines, the traditional way of teaching and learning should be transformed into electronic learning where ICT skills and technologies are introduced to the 21st-century learners, as well as 21st-century teachers. This paper tried to determine if teaching by utilizing Physics Education Technology (PhET) Simulations can impinge on the mastery of the least learned competencies in General Physics 1. It specifically analyzed the Proficiency level and Performance level in demonstrative applications in Physics. The current study also proposed an enhanced lesson plan exemplar that can be adopted by STEM teachers in teaching Physics. The descriptive method of research was employed in the study. During the investigation, there were 49 Grade 12 STEM students participated. The study concludes that PhET Simulation-Integrated instruction can improve the students' proficiency level on the least mastered competencies in General Physics 1. It also strengthened the claim that PhET Simulations can be a virtual laboratory for assessing students' performance on demonstrative applications. Further, utilizing and integrating PhET Simulations in delivering physics lessons can promote positive and engrossing learning experiences among learners.