A new approach of three-dimensional electro-chemical etchings both in vertical and lateral current directions on grid ditched Si pn-structures is originally proposed. Lateral etchings on the different ditched zones cause different porosities on porous Si, which emit visible lights of different wavelengths under ultraviolet light stimulation. Therefore, a single Si-based chip is capable of emitting visible light with tunable and multiple wavelengths simultaneously by this new approach. Moreover, the etching conditions on porous Si films and their related wavelengths can be fine-tuned by area sizes. Compared with the conventional method, the new approach provides a new option for multi-wavelength chip design with a precise patterning for porous Si without any mask and photoresist.