In this letter, we have studied the density of microtwins in the vicinity of the film surface, by using in-plane grazing incidence diffraction technique, to suggest a reduction trend of such defects at different growth rates. In (100) 3C–SiC heteroepitaxy, microtwin density decreases when a slower growth rate process is performed. A reduction ratio of microtwins of 0.16, 0.2, and 0.28 for 2 μm/h, 5 μm/h, and 10 μm/h, respectively, has been obtained. The relationship between microtwin density and growth rate, or Si/H2 ratio, found with this technique is in perfect agreement with the pre-existent literature.