  We report heating-compensated interlayer tunneling spectroscopy (ITS)
performed on stacks of overdoped Bi$_2$Sr$_2$CaCu$_2$O$_{8+x}$ intrinsic
junctions, where most of bias-induced heating in the ITS was eliminated. The
onset temperature of the pseudogap (PG), revealed in the hump structure of the
electronic excitation spectra, reached nearly room temperature for our
overdoped intrinsic junctions, which represented the genuine PG onset. At a
temperature below but close to $T_c$, both the superconducting coherence peak
and the pseudogap hump coexisted, implying that the two gaps are of separate
origins. The hump voltage increased below $T_c$, following the superconducting
gap voltage, which led to a conclusion that the hump structure below $T_c$ in
our ITS arose from the combined contribution of the quasiparticle spectral
weights of two different characters; one of the superconducting state and
another of the PG state near the antinodal region.
