In certain areas the Chinese are still around 40 years behind the Americans. Certain aspects of engine technology comes to mind. However, I think it is possible to correlate how far the Chinese are behind in particular field of fighter design, to how much this field was wider applications outside fighter design. The more specifically a field of technology narrowly applies to fighter design, the more likely the Chinese are further behind. The more broadly the field is applicable to other uses, the more likely the Chinese are either close to, or abreast of latest technology.
So I will venture to guess in the area of IR senior, semi-conductor design for AESA, and sensor fusion, the Chinese are not far behind at all, and may be almost breast of the best American technology. These are all areas the both have other applications, and readily benefit from advancements made for other applications.
In the field of solid rocket motor, and jet engines, the Chinese are likely further behind.