In this work, high quality epitaxial Si-doped InGaN films were grown on Si (111) substrate using plasma assisted molecular beam epitaxy (PAMBE) via controlling of Si flux. X-ray diffraction results showed controllable formation of c-axis Si:InGaN with different Si compositions, while XPS results indicate the Si was subsisted Ga site. Transmission electron microscope image showed the Si:InGaN films were grown epitaxially without phase separation with lattice mismatch between Si:InGaN and Si substrate of less than 1%. Photoelectrochemical (PEC) study was done under NaOH solution to achieve an optimum efficiency of 1.6% at 0V (vs. Ag/AgCl) with sample of Si flux at 6 x 10-9 torr. The series resistances of InGaN and Si:InGaN were reduced from 43.6Ω to 18.7Ω which was determined utilizing electrochemical impedance spectroscopy (EIS). The carrier concentration between Si:InGaN and InGaN were 9.4 x 1016 and 2.6 x 1018 cm-3, which was lead 2 times higher photocurrent density (0.8 and 1.6 mA/cm2, respectively) from Mott Schottky plot. Factors that might influence the PEC performance, such as the flat band position, crystallinity, and protons diffusion length will be addressed in this paper to obtain better insight into the issue of Si:InGaN for PEC. Keywords: plasma assisted molecular beam epitaxy, Si:InGaN, water splitting, carrier concentration Figure 1