In order for TMD such as molybdenum disulfide (MoS 2 ) to be useful for semiconductor industry, a controllable doping process is required. MoS 2 with substitutional Nb shows a p-type behavior compared to the n-type characteristics of nominal films. In this work, the role of Nb in MoS 2 will be examined, and a precise hole concentration control technique is demonstrated. Multi-layered Mo 1-x Nb x S 2 samples with accurately controlled Nb mole fraction are synthesized. Electrical characterization and material analysis are performed to quantify the impact of Nb with mole fraction from 3.5% to 11%. The effective carrier concentration (p) and the effective hole mobility (μ eff ) are found to be highly non-linear with respect to Nb mole fraction. Scanning Tunneling Microscope (STM) shows that the bandgap of the 2D transition metal dichalcogenide (TMD) is reduced by high mole fraction Nb. Therefore, Mo 1-x Nb x S 2 can be considered as a compound TMD semiconductor.