We have performed the first-ever, realistic 3D simulations of the photospheric structure of complete starspots, including their penumbrae, for a range of cool main-sequence stars, namely the spectral types M0V, K0V, and G2V. We used the MHD code MURaM which includes radiative energy transfer and the effects of partial ionization. We explore several fundamental properties like umbral intensity contrast, temperature, and magnetic field strength as functions of spectral type. Our simulations show that there is an increase in spot contrast with the increase in stellar surface temperature, which is consistent with observations. The umbral field strength is determined by the depth at which the optical surface forms and the surface pressures of the host stars. We will present our results and discuss the physics behind them.