This study sought to examine the benefits and values of implementing a Genre-Based Approach (GBA) in teaching the writing of explanation texts to senior high school students. It also aimed to investigate students’ perceptions of the implementation of GBA in the context of writing explanation texts. Adopting a case study design, the research collected data from classroom fieldnotes documenting the implementation of GBA, interviews, and students’ written texts. Data from the fieldnotes and interviews were analyzed using thematic analysis, whereas the students’ texts were examined through the Systemic Functional Linguistics (SFL) transitivity framework. The findings from the fieldnotes indicated that students initially experienced difficulties in understanding the teacher’s instructions delivered in English; however, the use of bilingual instruction during the implementation of GBA helped them to overcome this challenge. With regard to students’ writing performance, the GBA was found to be beneficial in improving their writing skills, as evidenced by their final texts, which successfully realized the three stages of the schematic structure of an explanation text and employed a range of linguistic features. Furthermore, the students’ responses revealed positive attitudes toward the teaching program, particularly toward the modeling and joint construction stages. Students reported that the explicit instruction provided in these stages was especially helpful for writing explanation texts, and gained new knowledge, experienced the stages of the writing process, and broadened their understanding of grammar.