SU-8 moulds have been widely used to cast polydimethylsiloxane(PDMS)microdevices.Differing from silicon and glass moulds,SU-8 moulds have to be fabricated on a substrate,and the adhesion performance between SU-8 and the substrate extremely influences the lifetime of SU-8 moulds.We developed a method for fabricating SU-8 moulds on glass substrates.A common thin negative photoresist was used as an adhesive layer and coated on the glass slide,and then SU-8 was patterned on the adhesive layer.The presence of the adhesive layer increased the lifetime of a SU-8 mould from a few cycles to over 50 cycles.The abilities of the method for replicating high-aspect-ratio microstructures were also tested.One SU-8 mould having micropillar arrays with aspect ratios lower than 3 could be used to cast over 20 PDMS microdevices.Moreover,while several methods have recently been developed to fabricate threedimensional SU-8 moulds,it is still challenging to build a multi-layer SU-8 mould with a width-decreasing cavity(e.g.,inverted T-shaped cavities)since some portion of the unexposed area of the lower SU-8 layer will be exposed if the upper SU-8 layer has a wider exposure area.Hence,we developed a method based on a sacrificial photoresist layer technique for fabricating a three-layer SU-8 mould with inverted Tshaped cavities.A positive photoresist was filled into the cavity formed by the first two-layer SU-8 to be a temporary substrate for the third SU-8 layer.The positive photoresist can be dissolved by the developer of SU-8.Thus,the sacrificial photoresist layer was easily removed with the development of the third SU-8 layer.To demonstrate this method,a PDMS sensing microchip with array of T-shaped cantilevers for studying the mechanics of cells was fabricated and tested.