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OSIRIS is a near-infrared integral field spectrograph operating behind the adaptive optics system at W. M. Keck Observatory. While OSIRIS has been a scientifically productive instrument to date, its sensitivity has been limited by a grating efficiency that is less than half of what was expected. The spatially averaged efficiency of the old grating, weighted by error, is measured to be 39:5% 0:8% at 1/2 1:310 µm, with a large field-dependent variation of 11.7% due to efficiency variation across the grating surface. Working with a new vendor, we developed a more efficient and uniform grating with a weighted average efficiency at 1/2 1:310 µmof 78:0% 1:6%, with field variation of only 2.2%. This is close to double the average efficiency and 5 times less variation across the field. The new grating was installed in 2012 December, and on-sky OSIRIS throughput shows an average factor of 1.83 improvement in sensitivity between 1 and 2:4 µm. We present the development history, testing, and implementation of this new near-infrared grating for OSIRIS and report on the comparison with the predecessors. The higher sensitivities are already having a large impact on scientific studies with OSIRIS. [ABSTRACT FROM AUTHOR]