Chemical etching for highly sensitive detection of defects in single- and polycrystalline silicon was investigated. Slow defect delineation was studied in a HF-HNO3-CH3CO2H system with CH3CO3H concentrations over 50% and micropit delineation etchants were developed. Micropit delineation etchants delineate defects with extremely small defect-energy and show good preferential etching ability. Micropit delineation etching was applied to electromagnetic cold crucible cast silicon and was found to reveal unknown micropits which conventional etchants failed to reveal. The high sensitivity to defect delineation by micropit delineation etching was explained by considering the ratio of defect etch rate to bulk etch rate. The electrical properties of the micropits were studied by monochromatic light-beam induced current measurement, which indicated that the micropits were electrically active.