The present disclosure is drawn to microfluidic devices. In one example, a microfluidic device can include a first covered fluid feed slot in fluid communication with a first microfluidic channel and a second covered fluid feed slot in fluid communication with a second microfluidic channel. The first microfluidic channel can be formed adjacent to the second microfluidic channel but not in fluid communication with the second microfluidic channel. The first covered fluid feed slot can include a first fluid feed hole for filling a fluid into the first covered fluid feed slot. The second covered fluid feed slot can also include a second fluid feed hole for filling a fluid into the second covered fluid feed slot.