Summary•Arabidopsis trichome formation is an excellent model for studying various aspects of plant cell development and cell differentiation. Our previous works have demonstrated that several C2H2 zinc finger proteins, including GIS, GIS2, ZFP5, ZFP6 and ZFP8, control trichome cell development through GA and cytokinin signalling in Arabidopsis.•We identified a novel C2H2 zinc finger protein, GLABROUS INFLORESCENCE STEMS 3 (GIS3), which is a key factor in regulating trichome development in Arabidopsis.•In comparison with wild-type plants, loss-of-function of GIS3 mutants exhibited a significantly decreased number of trichomes in cauline leaves, lateral branches, sepals of flowers, and main stems. Overexpression of GIS3 resulted in increased trichome densities in sepal, cauline leaves, lateral branches, main inflorescence stems and in the appearance of ectopic trichomes on carpels.•The molecular and genetic analyses show that GIS3 acts upstream of GIS, GIS2, ZFP8 and the key trichome initiation factors, GL1 and GL3. Steroid-inducible gene expression analyses and chromatin immunoprecipitation (ChIP) experiments suggest that GIS and GIS2 are the direct target genes of GIS3.