Wide band gap (WBG) alkaline-earth stannate transparent oxide semiconductors (TOSs) have attracted increasing attention in recent years for their high carrier mobility and outstanding optoelectronic properties, and have been applied widely in various devices, such as flat-panel displays. Most alkaline-earth stannates are grown by molecular beam epitaxy (MBE); there are some intractable issues with the tin source including the volatility with SnO and Sn sources and the decomposition of the SnO2 source. In contrast, atomic layer deposition (ALD) serves as an ideal technique for the growth of complex stannate perovskites with precise stoichiometry control and tunable thickness at the atomic scale. Herein, we report the La-SrSnO3/BaTiO3 perovskite heterostructure heterogeneously integrated on Si (001), which uses ALD-grown La-doped SrSnO3 (LSSO) as a channel material and MBE-grown BaTiO3 (BTO) as a dielectric material. The reflective high-energy electron diffraction and X-ray diffraction results indicate the crystallinity of each epitaxial layer with a full width at half maximum (FWHM) of 0.62°. In situ X-ray photoelectron spectroscopy results confirm that there was no Sn0 state in ALD-deposited LSSO. Besides, we report a strategy for the post-treatment of LSSO/BTO perovskite heterostructures by controlling the oxygen annealing temperature and time, with a maximum oxide capacitance Cox of 0.31 μF cm-2 and a minimum low-frequency dispersion for the devices with 7 h oxygen annealing at 400 °C. The enhancement of capacitance properties is primarily attributed to a decrease of oxygen vacancies in the films and interface defects in the heterostructure interfaces during an additional ex situ excess oxygen annealing. This work expands current optimization methods for reducing defects in epitaxial LSSO/BTO perovskite heterostructures and shows that excess oxygen annealing is a powerful tool for enhancing the capacitance properties of LSSO/BTO heterostructures.