The growth of a solid tumor in a confined microenvironment leads to increased compression, hypoxic/nutrition gradient within the tumor. However, Tumorspheres (TSs) cultured in free of spatial confinement do not exhibit physiological compressive stress. Here, we designed a microwell-based sphero-plate that allowed TSs to experience spatial confinement. On this platform, TSs underwent growth-mediated compressive stress and formed hypoxic cores. Moreover, drug resistance was enhanced by the hypoxia-inducible signaling and decreased by HIF-1 targeted drug within compact TSs. These findings highlight the impact of the design of the TSs-based drug testing platform.