CoFeW monolayers of different thicknesses were deposited on Si(100) substrates by DC magnetron sputtering, with CoFeW thicknesses from 10 to 50 nm. CoFeW thin films were annealed at three conditions (as-deposited, 250 °C, and 350 °C) for 1 h. The structural and magnetic properties were then examined by X-ray diffraction (XRD), low-frequency alternative-current magnetic susceptibility (χ), and an alternating-gradient magnetometer (AGM). The XRD results showed that the CoFe (110) peak was located at 2θ = 44.6°, but the metal oxide peaks appeared at 2θ = 38.3, 47.6, 54.5, and 56.3°, corresponding to FeO (320), WO (002), CoO (422), and CoO (511), respectively. The saturation magnetization (Ms) was calculated from the slope of the magnetization (M) versus the CoFeW thickness. The Ms values calculated in this manner were 648, 876, 874, and 801 emu/cm at the as-deposited condition and post-annealing conditions at 250, 350, and 400 °C, respectively. The maximum M was about 874 emu/cm at a thickness of 50 nm following annealing at 350 °C. It indicated that the M and the χ values rose as the CoFeW thin films' thickness increased. Owing to the thermal disturbance, the M and χ values of CoFeW thin films after annealing at 350 °C were comparatively higher than at other annealing temperatures. More importantly, the CoFeW films exhibited a good thermal stability. Therefore, replacing the magnetic layer with a CoFeW film improves thermal stability and is beneficial for electrode and strain gauge applications.