Miniaturization of semiconductor lasers holds the key to the development of compact, low-threshold, and fast coherent on-chip light sources/amplifiers, which are critically important for emerging applications in nanophotonics, integrated optics, and information technology (1–3). However, on-chip integration of nanoscale electronic components with conventional semiconductor lasers utilizing dielectric optical cavities is impeded by the diffraction limit-i.e., ∼(λ/2n)3 for three-dimensional (3D) cavities, where λ is the free-space wavelength and n is the refractive index of the dielectric (4–7). The recent advent of nanoplasmonics based on metallodielectric structures has led to the design of optical components and optoelectronic devices in the deep subwavelength regime (8–13). In particular, a new class of lasers based on surface plasmon amplification by stimulated emission of radiation (SPASER) has recently been proposed (14, 15) and experimentally demonstrated (16–19). In the SPASER operation, surface plasmons excited in noble-metal structures adjacent to gain media dramatically increase the optical mode density, shrink the optical mode volume, and provide the necessary feedback mechanism.