A high pressure osmotic dispense pump (10) having a substantially continuous delivery rate and extended delivery times is described and disclosed. The dispense pump (10) includes a semi-permeable membrane (12) which is substantially free of distortions and lateral stretching stresses. The membrane housing (14) and configuration of the present invention allows for consistent and accurate flow rates at the micro-liter level and improved control of the surface area of the semi-permeable membrane (12). This osmotic pump (10) also includes optional methods for activating and deactivating the osmotic process and/or controlling flow rates. Along with these features, the pump can be amplified or modulated to increase the dispense rate and/or adjust the flow rate during operation.