Figure out how you've improved yourserlf and how you have added value to your department or company, then figure a good way to present it to your boss.
Email or ask to have a meeting set aside on such and such a day to discuss your compensation. Meet, present, and if your company is like my previous, they'll turn you down and tell you "we are paying you at 95% of our already fixed paygrade "midpoint" for your arbitary engineering level based on nothing but time served, so you don't get a raise-wait until year end when everyone else gets their raises and we'll give you up to 2% if you are an all-star!"
If they are decent and you are doing a good job, learning alot, adding value, and present it well, I'd like to think you'll get that raise.
If you don't get a raise, and it's not some HR type crap reason, then ask how you have to improve to increase your compensation. If your boss can't tell you, find a new boss because he won't be worth any type of career development for you.
I may sound cyincial but I just lived through this same scenerio several times with my past employer/supervisor. I worked in a high activity area with very little senior engineering support, so it was a "learn as much as you can as fast as you can" environment. I saw projects like no one in our company had ever seen, including the senior engineers in other locations. My boss actually told me and three other engineers standing nearby that we could be replaced off the street by a new grad tomorrow that was just as productive. Well, it's been 4 months since I gave notice, 3 since I left, and he has yet to find a suitable replacement. Sad part is, it was my engineering partner that is feeling the brunt, the boss hasn't missed a lick... He still getting his bonuses and big raises. Dilbert through and through.
But, fight the fight and good luck!