Using metalorganic vapor phase epitaxy to grow GaInAs/InP layers on masked InP substrates patterned with submicron square holes, we have fabricatedinsituburied quantum dot arrays for the first time. Starting with mask openings ≥150 nm × 150 nm and utilizing the natural crystal habits to form low‐index plane facetted pyramids inside the holes, <m1;&40q>highly regular GaInAs quantum dots embedded in InP are obtained in a single growth step. <m1;&40q>As verified by cathodoluminescence, the dots exhibit very high luminescence efficiencies, even at room temperature, owing to the absence of air‐exposed or etch‐damaged heterointerfaces.