Our first quarter results reflect continued solid execution by our operations and robust demand for our services. Our revenues in the first quarter grew 68% compared to the first quarter of 2011, and our GAAP diluted earnings per share of $0.22 represents a $63.3 million net income improvement over the same quarter last year. Both our 12 month and total backlog increased at the end of the first quarter compared to the end of the same quarter in 2011. 12-month backlog increased about 37% and total backlog increased almost 12% compared to the backlog at the end of the first quarter of 2011.
Our first quarter results were driven by strong performance in our Electric Power segment, due to the number of electric transmission projects in construction and our ability to safely execute on these projects. Of note, our void count at the end of this year's first quarter was about 19,000, up 35% compared to the first quarter of last year, and up 7% sequentially since the end of the fourth quarter of 2011.
Turning to our Electric Power segment, revenues increased approximately 65% in this year's first quarter compared to the same period last year. 12-month backlog at the end of the first quarter for the Electric Power segment increased 45%, and total backlog for this segment increased 14% compared to the end of the 2011 first quarter. We are in the construction phase on 12 large electric transmission projects, and most are progressing as expected without significant delays. We continue to see significant opportunities for large electric transmission awards in 2012 and 2013, as utilities move forward with these projects to improve grid reliability and transport power from renewable sources to load centers. We believe we are still in the early stages of a multiyear transmission build-out in the United States and Canada, and expect our Electric Power segment backlog to remain strong throughout 2012 and beyond. We are currently in various stages of discussions on approximately $1 billion of large electric transmission projects that we expect will be awarded this year.