When a number of TEMs (thermoelectric modules) are connected in a series-parallel matrix and under mismatched temperature gradients, the overall maximum output power of the thermoelectric generator (TEG) may be lowered by certain TEMs with relatively smaller temperature difference. It is possible to avoid such a performance decrease by the disconnection of these low temperature TEMs, provided that the critical power point can be accurately determined. In this paper, firstly a rigorous and universal formulation is fully detailed to mathematically determine the conceptions and conditions of the critical power point in the series and parallel TEM arrays. Secondly, experiments of a series-parallel hybrid interconnected TEG are presented to clearly quantify the theoretical analyses. Finally, the hierarchical simulation, based on the SPICE (simulation program with integrated circuit emphasis) platform, is applied to estimate the critical power point. By numerically modeling the nonlinear physical processes of the TEG, the simulation can be used as an enabling technique in any model-based controller to dynamically minimize the mismatch power loss within the TEM matrix of any configuration. In experimental and numerical results, a number of critical power points are disclosed for a 2×4 parallel-serial hybrid TEM matrix, where the hot temperature mostly ranges from 120°C to 60°C.