We fabricate MgB2 ultra-thin films via hybrid physics-chemical vapor deposition technique (HPCVD). Under the same background pressure, the same H2 flow rate and the same deposition time, by changing the B2H6 flow rate, we fabricate a series of ultra-thin films with thickness values ranging from 10 nm to 40 nm. These films grow on MgO(111) substrate, and are all c-axis epitaxial. These films show the good connectivity, a very high Tc(0) ≈ 35-38 K and a very low residual resistivity ρ(42 K) ≈ 1.8-20.3 μΩ·cm-1. As the thickness increases, critical transition temperature also increases and the residual resistivity decreases. The 20 nm film also shows an extremely high critical current density Jc (0 T, 5 K) ≈ 2.3×107 A/cm2, which indicates that the films fabricated by HPCVD are well qualified for device applications.