In this Chapter, we summarize the current status and future prospects of a number of novel semiconductor-based single-photon detectors, including visible-light photon counters (VLPCs), solid-state photo-multipliers (SSPMs), and quantum-dot-based detectors. SSPMs and VLPCs utilize the gain produced by impact ionization of the impurity band to detect single photons over a wide wavelength range between 0.4 and 28. Quantum-dot-based single-photon detectors use photoconductive gain associated with photogenerated carriers trapped in quantum dots. We cover the basic operating principles of these devices, describe experimental results that demonstrate their unique attributes, present mathematical models that quantify their performance, and discuss the future of these novel detector technologies.