Generally oriented mesas and pyramidal-shaped objects were patterned in (1 0 0) InP substrate by etching in 3HCl: 1H 3 PO 4 at (16±0.05) C through convex InGaAs mask patterns. The mesas were revealed through long (∼ 2 mm) parallelogram-shaped mask strips whose long edges lay between [0 1 1] and at a variable angle ω, with ω≡ 0 at [0 1 1]. The mesas were re-entrant for ω epsilon [0, 45) and ordinary for ω epsilon (45, 90]. The tilt of mesa side facets α and the associated mask underetching rates were evaluated using SEM, AFM and optical microscopy. The underetching rate was zero at ω= 0 and 90. With|(ω− 45)|→ 0 it increased asymmetrically about [0 0 1]: for|(ω 1− 45)|=|(ω 2− 45)| it was higher at ω 1< 45 than at ω 2> 45. At ω= 45.5 ordinary (1 1 0)-and-related facets, tilted at α≈ 45, were revealed at a rate of (310.1±8.1) nm min− 1. Likewise at ω= 45.5 off [0 1 1] to (1 0 1)-and-related facets formed. In theory,(1 1 0),,(1 0 1) and define a pyramidal shape with the sides tilted at 45 to (1 0 0). In practice, an object confined by facets related to (1 1 0),,(1 0 1) and cannot be revealed via a convex-cornered lozenge-shaped pattern with the edges at ω= 45.5 and diagonals parallel with [0 1 1] and because the'pyramidal'facets are suppressed by fast-etching re-entrant facets that form at the-and-oriented corners. If compensated with eg rectangular strips, the pyramidal facets can be revealed at the lozenge edges. Etch-stop (2 1 1) A-related facets were formed along the compensation strip edges and fast-etching re-entrant facets at the convex corners of the compensation strips. The angular orientation of the pyramidal facets slightly shifted with etching time: the normal vector of the top pyramidal facet edge deviated off⟨ 0 0 1⟩ towards [0 1 1] or from (1.13±0.14) at t etch= 2 min to (2.32±0.10) at t etch= 10 min. Concurrently, the tilt of the'pyramidal'facets α to (1 0 0) decreased from (45.35±0.04) for t etch= 2 min to (44.16±0.06) for t etch= 10 min.