A new approach to blind and semi-blind channel estimation for space-time block codes (STBCs) is presented. By exploiting the recently proposed generalized space-time block code framework, an STBC system is reduced from multiple-input multiple-output to a single-input multiple-output system. A conventional blind algorithm based on the subspace algorithm is then used to identify the channel impulse responses and achieve equalization. Simulation results demonstrate the performance of the proposed algorithm and a comparable scheme.