We investigated the optical properties of Ag hemisphere-like nanoparticles. The nanoparticles were prepared by using magnetron sputtering and post-thermal annealing. The scanning-electron microscopy images reveal that hemisphere-like nanoparticles were successfully produced. The transmission spectra exhibit the surface plasmon resonance effect. From the spatial intensity distributions obtained by solving Maxwell equations using the three-dimensional, finite-difference time-domain method, we found that there is strong confinement of the optical field near the nanoparticle. This optical confinement makes it easy to exhibit the plasmon resonance effect.