For the switching performance of low-voltage (LV) power MOSFETs, the gate-drain charge density (Qgd) is an important parameter. The so-called figure-of-merit, which is defined as the product of the specific on-resistance (Rds,on) and Qgd is commonly used for quantifying the switching performance for a specified off-state breakdown voltage (BVds). In this paper, we analyzed the switching behavior in power trench MOSFETs by using experiments and simulations, focusing on the charge density Qgd. The results of this analysis can be used for further optimization of these devices. The results show that the Qgd can be split into three charge contributions: accumulation, depletion, and inversion charge. It is shown that the inversion charge is located mainly underneath the trench bottom. The accumulation and depletion charge contribute each about 45% in conventional LV trench MOSFETs and can be reduced by using a thick bottom oxide in a shallow trench gate just extending in the drift region. Further, we derived an analytical model for calculating the Qgd, that takes into account the geometry dependence.