There are many ways you can improve your leaps/Saut de Chat. Most importantly dancers need a good balance of strength and flexibility in order to achieve a full split in the air. Sometimes, dancers have both of these things, but still lack the 180 degree range. There are many methods used to teach leaps, but we're hoping this one clicks with you.
The leap is only as high as the passe. A Saut De Chat or leap, unlike a grand jete, passes through passe before straightening. If your passes are low when you extend your leg, ypur leg will remain at that low level. Instead, try to have the highest passe possible. This high passe has a greater chance of remaining high during the completion of the saute chat/leap. With the front leg reaching a full 90 degrees at extension, you are free to work on getting your back leg up- along with the other necessary leaping technique. See the below pictures: