Pin fins have the potential to improve the thermal performance of various engineering devices. Modified pin fins could further increase their thermal performance in a passive way at lower cost. This study is aimed to numerically investigate the thermal performance of trenched hemispherical pin fins heat sink (THPFHS) and the influence of parameters including the trench number (N=1, 3 and 5) and thickness (e =1 to 5 mm). The simulations are performed using a CFD software considering turbulent air flow conditions. Results show that the use of aluminum fins fitted with one trench in the middle of the hemispherical pin fin considerably increases the local heat transfer. Furthermore, all studied configurations show high thermal performance factor (HTPF) compared with the conventional CPFHS (cylindrical pin fins heat sink). For this new configuration (THPFHS), Nu increases by 45% while the thermal resistance reduces by 42%, compared to the baseline case. On the other hand, this improved performance results in 50% pressure drop penalty. Moreover, the obtained results show a significant improvement in the performance mainly at high Re.