Thermoelectric (TE) generators play an important role in preventing an energy crisis and environmental deterioration by converting wasted heat, generated by various human activities, into electrical energy. This work is the first experimental demonstration of a bileg Si-nanowire (Si-NW) micro thermoelectric generator with cavity-free architecture for designing a large-scale integrated planar Si-NW TE generator. In the bileg-TE generator, the mobility and thermopower mismatches between electron and hole effects on the optimum dimensional parameters of n- and p-type Si-NWs and optimum dose of impurity. In this work, under a specific ion dose condition, the best p-type NW width exists at less than 100 nm when the n-type NW width is 60 nm. The experimental dependency of the power density on the p-type NW width is in agreement with the estimation of an equivalent heat-electrical circuit model.