SPIFFI is the integral field spectrograph of the VLT- instrument SINFONI. SINFONI is the combination of SPIFFI with the ESO adaptive optics system MACAO offering for the first time adaptive optics assisted near IR integral field spectroscopy at an 8 m-telescope. SPIFFI works in the wavelength ranger from 1.1 to 2.5 micrometers with a spectral resolving power ranging from R equals 2000 to 4500. Pixel scale ranges from 0.25 to 0.025 seconds of arc. The SPIFFI field- of-view consists of 32 by 32 pixels which are rearranged with an image slicer to a form a long slit. Base don the 3D slicer concept with plane mirrors, an enhanced image slicer was developed. The SPIFFI image slicer consists of two sets of mirrors, called the small and the large slicer. The small slicer cuts a square field of view into 32 slitlets, each of which is 32 pixels longs. The large slicer rearranges the 32 slitlets into a 1024 pixels long slit. The modifications to the 3D slicer concept affect the angels of the plane mirrors of small and large slicer and lead to an improved slit geometry with very little light losses. At a mirror width of 0.3 mm the light loss is < 10 percent. All reflective surfaces are flat and can be manufactured with a high surface quality. This is especially important for the adaptive optics mode of SINFONI. We explain the concept of the SPIFFI mirror slicer and describe details of the manufacturing process.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.