This research explores the behavior of CoFeWB when it is sputtered onto Si(100) substrates with a thickness (t) ranging from 10 nm to 100 nm, and then altered by an annealing process at temperatures of 200 °C, 250 °C, 300 °C, and 350 °C, respectively. The crystal structure and grain size of CoFeWB films with different thicknesses and annealing temperatures are observed and estimated by an X-ray diffractometer pattern (XRD) and full-width at half maximum (FWHM). The XRD of annealing CoFeWB films at 200 °C exhibited an amorphous status due to insufficient heating drive force. Moreover, the thicknesses and annealing temperatures of body-centered cubic (BCC) CoFe (110) peaks were detected when annealing at 250 °C with thicknesses ranging from 80 nm to 100 nm, annealing at 300 °C with thicknesses ranging from 50 nm to 100 nm, and annealing at 350 °C with thicknesses ranging from 10 nm to 100 nm. The FWHM of CoFe (110) decreased and the grain size increased when the thickness and annealing temperature increased. The CoFe (110) peak revealed magnetocrystalline anisotropy, which was related to strong low-frequency alternative-current magnetic susceptibility (χ) and induced an increasing trend in saturation magnetization (Ms) as the thickness and annealing temperature increased. The contact angles of all CoFeWB films were less than 90°, indicating the hydrophilic nature of CoFeWB films. Furthermore, the surface energy of CoFeWB presented an increased trend as the thickness and annealing temperature increased. According to the results, the optimal conditions are a thickness of 100 nm and an annealing temperature of 350 °C, owing to high χ, large Ms, and strong adhesion; this indicates that annealing CoFeWB at 350 °C and with a thickness of 100 nm exhibits good thermal stability and can become a free or pinned layer in a magnetic tunneling junction (MTJ) application.