In this study, the effect of thickness on the Sn-doped β-Ga2O3 thin films was investigated. β-Ga2O3 is a next-generation material for power semiconductors and optoelectronics owing to its remarkable properties, such as an ultra-wide bandgap, excellent thermal and chemical stability, and large breakdown voltage. However, its inherently low conductivity can be limiting in applications that require high conductivity; therefore, improving the conductivity of β-Ga2O3 is important. In this study, Sn-doped β-Ga2O3 thin films with various thicknesses were deposited on β-Ga2O3 substrates. All the fabricated samples exhibited β-phase with a uniform and dense surface and transmittance of above 80% in the visible region. In particular, the 100 nm samples showed the highest carrier concentration and mobility and the lowest resistivity. Thus, these findings are expected to play an important role in improving the performance of devices by controlling the thickness of thin films.