This work demonstrates a cavity-free micro thermoelectric generator (TEG) consist of Si nanowires (Si-NWs) . In the cavity free structure, one side of TEG is heated by the structure of metal overlayer, called Heat Guide (HG), to supply heat selectively to specific microregions within the device. Thus, heat energy flows in the perpendicular direction which forms steep temperature gradient in the NWs. However , the performance can be varied with the various thickness of HG. In this work, we fabricated integrated device with different HG thicknesses and investigated their effects on power generation performance. The result revealed that with thicker HG, the integrated device exhibits higher power generation performance.