© 2020, Emerald Publishing Limited.Purpose: The aim of this paper is to investigate the conjugate forced convection in a semi-cylindrical cavity with air flow. Isotherms, streamlines, Bejan number and local entropy generation number are obtained for the semi-cylindrical cavity. Local Nusselt number, the temperature and the skin friction along the interface wall are calculated with different Reynolds numbers and geometric configurations. Design/methodology/approach: The governing differential equations discretized by finite volume method are solved using SIMPLE algorithm. In this study, collocated grid, where all flow variables are stored at the same location, is used. Alternating direction implicit method and tri-diagonal matrix algorithm are used to solve linear algebraic equation systems. Findings: The effects of Reynolds numbers, inlet and exit cross-section, the locations of exit section on fluid flow are also numerically investigated. It has been observed that since the secondary vortices developed near the exit cross-section negatively affect heat transfer, the temperature value is higher at this region. Better cooling inside cavity is provided in the cases of higher Re number, larger inlet and exit cross-section. The minimum average Nu numbers are computed for the location of L = 0.40 and the minimum total entropy generation numbers are founded in the case of L = 0.20. Originality/value: This study provides insight into proper cooling and entropy generation inside the semi-cylindrical cavity for different conditions.