We have developed a new method of laser-assisted nanoimprinting to fabricate hemispherical-cavity arrays on silicon (Si) and germanium (Ge) substrates. A monolayer of silica particles, with different diameters ranging from 0.30 to 5 μm, was deposited on a Si or Ge substrate by self-assembly technique. A quartz plate was tightly placed on the sample surface to form a quartz/nanoparticle/substrate structure. The silica particles were imprinted into Si or Ge substrates after laser irradiation (KrF excimer laser, λ=248 nm) on the structure with a single pulse. Ultrasonic cleaning and hydrofluoric-acid (HF) solution were used to remove the silica particles on the substrate surface. Hemispherical cavities were formed on the substrate surface. The influences of different particle size and laser fluence on the structuring of the surface have been investigated. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) were performed to observe the dimensions of the cavities. One-dimensional thermal calculation was employed to understand the thermal effects in this process.