A cooling device comprises a first casing for direct mounting on a heat-generating component and a second casing mounted on the first casing. One casing includes an internal channel connected to a cold inlet and to a hot outlet allowing a heat-transfer fluid to flow in the internal channel. The other casing includes a storage containing a phase change material (PCM) changing from a solid state to a liquid state to transfer thermal energy from the heat-generating unit to the PCM, the PCM changing from the liquid state to the solid state to transfer thermal energy from the PCM to the heat-transfer fluid. The cooling device may be integrated in a cooling circuit of a cooling system including an external cooling unit, or in a closed loop cooling circuit of a cooling arrangement that transfers heat from the closed loop to an open loop.