To understand fully the operating mechanism of three‐terminal semiconductor devices, it is important to know the minority‐carrier, electric field, potential, and current‐density distributions within the device as a function of the spatial variables. This paper presents the formulation and closed‐form solution of the two‐dimensional dependency of the minority‐carrier distribution within a three‐terminal semiconductor device and in particular as it applies to the thyristor. Boundary conditions to obtain the solution were chosen so as to conform to realistic devices being manufactured and to the physical properties of their surfaces. The general solution was derived starting from the basic diffusion equation, and family of curves of the solution for the static case of typical thyristors were obtained with the aid of a digital computer. This was done for the forward blocking and forward conducting states with and without gate current. Experimental results were carried out and good correlation with analytical calculations were obtained.