The design of piezoelectrically actuated plano-convex shaped resonators has been studied to optimize their Q-factor and signal spectrum at high temperatures. The investigated arrays of thickness-shear-mode (TSM) resonators consist of langasite, a high temperature stable material. As viscoelastic damping and an increasing conductivity decreases the Q-factor at elevated temperatures, design optimizations have to counteract these effects. Two and three dimensional finite element (FE) models have been solved to analyze the resonant behavior and the effects of energy confinement at different temperatures depending on geometry. The separation and suppression of spurious modes, the improvement of the Q-factor and the confinement of the TSM could be shown. The simulated effects of energy confinement could be proofed by impedance measurements.