SpriteFont mFont;
SpriteBatch mSprite;
mSprite.Begin();
mSprite.DrawString(mFont, "YourText", new Vector2(graphicsDevice.Viewport.Width / 2 - mFont.MeasureString("YourText").Length() / 2, 0), Color.White, 0, new Vector2(0, 0), 1f, SpriteEffects.None, 0f);
mSprite.End();