The walkoff-compensated (WOC) twin-crystal device enables to reduce the aperture effects in critically phase-matched parametric generation. In that device, instead of using a monolithic bulk crystal of length 21 c, two identically-cut crystals of length l c are disposed in tandem such that the relative sign of the walkoff angle ρ in the first and second items are opposite, while keeping unchanged the relative sign of their non-linear effective susceptibilities through a proper orientation of their optic axes. Applied to KTiOPO 4 (KTP) for type-II (oeo) second-harmonic generation (SHG) of a color center laser, the 2 × l c twin- crystal device leads to a conversion efficiency 3.5 times higher than that of a 21c single bulk crystal. The same WOC technique has been applied successfully in the type-I (ooe) SHG of a CO 2 laser using an AgGaSe 2 (AGSE) device. The extension of the WOC method to a periodical structure composed of N twin-device stacks is considered. We report the first demonstration of the SHG efficiency enhancement of such a structure, which is made of four KTP plate optically contacted in the WOC configuration.