This study aimed to develop and validate an inventory that measures the whole range of basic and integrated science process skills as stipulated in the Malaysian science curricula and that is suitable for Malaysian lower secondary school students. The validated inventory was subsequently utilised to determine the differential acquisition of science process skills by gender, location, and ethnicity. In the instrument development phase which involves item generation and field testing, a reliable 60-item Malaysian-Based Basic and Integrated Science Process Skills Inventory (MB-BISPSI) that has a KR-20 reliability of 0.88, difficulty indices of items that range between 0.25-0.75 and discrimination indices which are above 0.4 was produced. In the main causal-comparative study using a sample of 1021 Form 2 students (548 girls and 473 boys) from seven (four rural and three interior) out of the eight secondary schools in Kapit Division, Sarawak, the findings indicate that the students achieved a mastery level which fell short of the two-third benchmark (e.g., 66.7%) for the overall science process skills, basic and integrated science process skills, and also for each of the 12 science process skills. Additionally, it was found that, while female students generally achieved a markedly higher mean percentage score in the overall Science Process Skills than did the male students, such phenomenon was only observed amongst the Kenyah ethnicity. There were no significant differences in science process skills acquisition between rural and interior students. Implications for a more thoughtful inculcation of science process skills are proffered alongside recommendations for future research using a more nationally representative sample to examine the validity of such generalisation.