We present a theory of absorptive electro‐optic spatial light modulators based on GaAs/AlGaAs multi‐quantum well structures using arbitrary potential well profiles. In particular, we consider three different quantum well profiles: square, parabolic, and asymmetric triangular. We calculate the transition energies, oscillator strengths and absorption co‐efficients of the lowest‐lying heavy‐ and light‐hole excitons as a function of well width and electric field using a variational approach assuming decoupled valence subbands. For illustrative purposes we select the photon energy of the monochromatic source to be modulated at 1572 meV and aluminum concentration in the barriers to be 0.3. For the sake of comparison among the various modulators with different quantum well profiles we assume that this photon energy coincides with the lowest‐heavy‐hole exciton transition in the absence of an electric field. We find that the required well widths are 75 A˚ for the square well, 174 A˚ for the parabolic well, and 676 A˚ for the asymmetric triangular well. At zero electric field the values of the exciton oscillator strengths in all three quantum well systems are comparable. However, superior performance in terms of higher contrast ratio is obtained in the case of modulators based on asymmetric triangular wells. For instance, in the case of a square well with excitonic linewidth of 3 meV, a field of approximately 50 kV/cm is required to achieve a 30% decrease in absorption. On the other hand, the field required to achieve the same change in absorption in a parabolic well is 35 kV/cm and in an asymmetric triangular well is −7 kV/cm. The contrast ratio at an electric field of −20 kV/cm is 6.7 for an asymmetric triangular well and 1.02 for a square well in a multi‐quantum well sample where the contacts are 2 &mgr;m apart.