Soil heat flux G_s is an important component of the surface energy balance. Soil heat flux plates (SHFPs) are widely used to measure G_s, although several errors are known to occur. The Philip correction has been applied to minimize errors in G_s measured by SHFPs (G_p) if the soil thermal conductivity λ_s, SHFP thermal conductivity λ_p, and plate geometry function H are known. The objective of this study is to evaluate the effectiveness of the Philip correction for a variety of SHFPs. The λ_p were determined without thermal contact resistance and differed from the manufacturer-specified λ_p. A simplified H formulation was similar to or less than the full H equation for different SHFP shapes. The G ratio (G_p/G_s) was sensitive to λ_s/λ_p and H when they were relatively small. Compared with the G_s determined by a gradient method (G_s_grad), the G_pmeasured under a full corn (Zea mays, L.) canopy in the field underestimated G_s by 38%–62%. After applying the Philip correction, almost all G_p agreed better with G_s_grad. Generally, the G_p corrected with measured plate parameters agreed better with G_s_grad than those corrected with manufacturer-specified values. The G_p corrected with the simplified and full H expression differed for different SHFPs. These results indicate that SHFPs always underestimate G_s and that the performance of the Philip correction is affected by λ_p, plate dimensions, and H. An alternative method to measure G_s by a three-needle heat-pulse sensor or a gradient method, in which soil temperature and water content are measured at several depths, is recommended.