The microelectromechanical systems technologies frequently produce rough surfaces, and the repercussion of roughness on the thermal performance is more prominent in structures of smaller dimensions. In this regard, the present article intends to examine the unsteady thermal behavior of a fully wet, porous, and rough micropin‐fin structure under convective–radiative conditions. Here, a pin fin of a cylindrical profile has been chosen. The problem is modeled by incorporating the roughness parameters in the perimeter and cross‐sectional area of the pin fin. Further, the study of the porous structure has been carried out by implementing the Darcy model. The resulting partial differential equation is nonlinear and of the second order which has been solved by employing the finite difference method. The impact of the roughness parameter, wet porous parameter, dimensionless time, convective parameter, base radius‐to‐length ratio, radiative parameter, thermal conductivity parameter, power index, and ambient temperature on the thermal performance and efficiency of rough micropin‐fin structures has been established graphically. According to the findings, for 0.15% $0.15 \% $ rise in roughness, the rough micropin fin has 12% $12 \% $ more thermal drop rate and 13% $13 \% $ less efficiency than the smooth one. Further, the work is beneficial in the field of microelectronics, especially in the design of micropin‐fin structures.