Silver (Ag) paste is widely used in semiconductor metallization, especially in silicon solar cells. Ag powder is the material with the highest proportion in Ag paste. The morphology and structure of Ag powder are crucial which determine its characteristics, especially for the sintering activity. In this work, a simple method was developed to synthesize a type of microcrystalline spherical Ag particles (SP-A) with internal pores and the structural changes and sintering behavior were thoroughly studied by combining ultra-small-angle X-ray scattering (USAXS), small-angle X-ray scattering (SAXS), in-situ heating X-ray diffraction (XRD), focused ion beam (FIB), and thermal analysis measurement. Due to the unique internal pores, the grain size of SP-A is smaller, and the coefficient of thermal expansion (CTE) is higher than that of traditional solid Ag particles. As a result, the sintering activity of SP-A is excellent, which can form a denser sintered body and form silver nanoparticles at the Ag–Si interface to improve silver silicon contact. Polycrystalline silicon solar cell built with SP-A obtained a low series resistance (R_s) and a high photoelectric conversion efficiency (PCE) of 19.26%. These fill a gap in Ag particle structure research, which is significant for the development of high-performance electronic Ag particles and efficient semiconductor devices.