Some high-performance mobile devices use aggressive thermal throttling to control the temperatures of the processors inside the device. As the device heats up it intentionally slows the processor to avoid overheating, which in turn leads to lower performance scores on successive runs. Measuring the effects of thermal throttling is another interesting way of using 3DMark to compare the performance of different devices.
To reduce this effect, we recommended waiting 15 minutes between runs to allow the device to cool down. You should also unplug the device during testing as the battery charging circuitry also generates heat. Try running the test in a cool environment. Don't run the benchmark in direct sunlight or near sources of heat. For more tips on getting the best results from your device, please see our How to Benchmark page.