The main concern of this study was to investigate the effects of integrated reading and writing skills instruction on EFL learners' critical thinking skills achievement at Bahir Dar University. At this point, a quasi-experimental research design was employed, and 96 English majoring students as experimental (n = 48) and control (n = 48) groups participated in the study with a random assignment. Herein, the experimental group was instructed through integrated reading and writing skills instruction and the control group with the conventional method for consecutive 12 weeks, and then, 25 (twenty-five) pre and post-tests of critical thinking questions were employed to assess students’ achievement. Data were collected through tests, and then the Kappa inter-rater reliability and split-half tests were employed to compute the reliability and internal consistency of both tests respectively. Finally, the data were analyzed using an independent t-test, and then the result of the pre-test revealed that both experimental and control groups were homogenous in critical thinking skills’ achievement. However, after the treatment, the post-test results depicted that the experimental group significantly outscored the control group. In a nutshell, the study showed the supremacy of integrated reading and writing skills instruction over the conventional approach in enhancing students’ critical thinking skills achievement