Intense photoluminescence (PL) was observed from a new class of Si‐based quantum well structures (QWs), that is, neighboring confinement structure (NCS). NCS consists of a single pair of tensile‐strained‐Si layer and a compressive‐strainedSi1−yGeylayer sandwiched by completely relaxedSi1−xGex(layers.Inspiteoftheindirectbandstructureinrealandkspaces,radiativerecombinationwasenhancedcomparedwithnotonlytype‐IIstrained‐Si/relaxed‐Si1−xGexQWs but also type‐I strained‐Si1−yGey/relaxed‐Si1−xGexQWs. PL without phonon participation was found to dominate the spectrum possibly due to the effective carrier confinement for both electrons and holes. Quantum confinement effect was clearly observed by varying the well width, showing that the expected band alignment is realized. ©1995 American Institute of Physics.