We present a microcanonical kinetic theory, which we refer to as the lth-order semi-Markov phase space theory (SMl-PST), for nonadiabatic unimolecular dissociations dominated by standard surface hopping dynamics. In this theory, reaction dynamics is considered as a stochastic transport, which is described as an lth-order Markov chain, among cells produced from partition of the available phase space. Kinetic equations are derived by importing residence time of stay cells as a random variable into the Markov chain. An efficient method to determine the parameters of the kinetic equations is developed, which is made up of Monte Carlo phase space integration and short-time trajectory calculations. As a test calculation, the SMl-PST has been applied to a model system for the predissociation of collinear N2O. We show that the SMl-PST works well, giving rate coefficients of much better accuracy than conventional statistical theory and of comparable accuracy to standard trajectory calculations with a lower computational effort.