InGaN-based laser diodes (LDs) grown on the semipolar (20 (2) over bar(1) over bar) plane of GaN offer advantages arising from predicted higher gain compared to c-plane devices. However, the performance of semipolar devices has been limited by low injection efficiency. In prior work, this has been proposed to be caused by an inefficient AlGaN electron blocking layer (EBL). A high oxygen level in the EBL found in previous work could cause compensation of the p-type dopants. In this work the oxygen impurities were eliminated via optimizations during the metalorganic chemical vapor deposition (MOCVD) growth. Optimization of the V/III ratio and an increase in the growth temperature during the AlGaN growth was found to reduce the oxygen incorporation. Additionally, residual sources of oxygen were removed from the MOCVD growth process. These combined steps reduced the peak oxygen level in the AlGaN from 5x10(18)/cm(3) to 6x10(17)/cm(3) as measured by secondary ion mass spectroscopy. LDs were fabricated with and without these modifications to clarify the effect of the reduced oxygen. The threshold current and differential efficiency showed improvement with reduced oxygen. The internal loss and gain of these LDs were measured using the segmented contact method, confirming that the injection efficiency was boosted from 60% with high oxygen to 80% with low oxygen.