A thermal energy harvester using piezo-shape memory alloy (SMA) composite was designed. The main mechanism of such a piezo-SMA composite is the synergistic effect of piezoelectrics and SMA, which are connected in series and subjected to fluctuating temperature. Strain induced in the SMA phase immediately causes stress in the piezoelectric phase, thus, inducing charge by the direct piezoelectric effect. In order to make this problem more analytically tractable, two models were developed: simple laminated model and 3D model with Eshelby theory. The models predict the available power according to material properties and thermal fluctuation. The impedance of the system was examined with different thermal fluctuating frequencies. Experimental and predicted results are in agreement for higher frequencies, while for lower frequencies of thermal fluctuation, the prediction is not accurate due to internal loss.