In this research, we have investigated the deposition condition of pentacene film on nitrogen doped (N-doped) LaB6 donor layer for larger grain growth at the channel region for bottom-contact type pentacene-based organic field-effect transistors (OFETs) to improve the device characteristics. Source and drain bottom-contacts of Al were patterned and 2nm-thick N-doped LaB6 donor layer was deposited on the SiO2/Si(100) back-gate structure. The dendritic grain growth of pentacene larger than 10µm without lamellar grain growth was demonstrated when the deposition temperature and rate were 100°C and 0.5nm/min, respectively. Furthermore, it was found that the dendritic grain growth was realized at the boundary region of bottom-contact as well as channel region.