Abstract: High-speed boundary layer transition directly affects the aerodynamic force and aerodynamic design of high-speed vehicles. Local wall temperature variations can influence this transition process; however, the underlying mechanisms remain to be further investigated. In this study, experiments were conducted in a Mach 6 Ludwieg tube wind tunnel using a 7° half-angle sharp cone model at zero angle of attack. High-frequency pressure sensors, a high-speed infrared camera, and a focused laser differential interferometer are employed to investigate the effects of cone tip temperature variations on the instability of high-speed boundary layers. The results provide valuable data support for the thermal protection and aerodynamic design of high-speed vehicles. The experimental results indicate that when the region of tip temperature variation is located upstream of the synchronization point, cooling of the cone tip enhances the nonlinear interaction of the second-mode instability waves, increases their saturated amplitude, and ultimately delays boundary layer transition; conversely, heating of the cone tip suppresses the nonlinear interaction of the second-mode instability waves, reduces their saturated amplitude, and thus promotes boundary layer transition. Infrared measurements further show that tip cooling reduces the surface temperature difference at transition, while tip heating produces the opposite effect.